With advancement of the wireless communication technologies, requirements on wireless communication devices become ever higher. For antennas that function to transmit and receive electromagnetic (EM) signals, a number of structures have been developed to satisfy requirements of the communication devices. This imposes greater challenges in terms of performances or structures of the antenna.
An antenna acts as a transmitting unit and a receiving unit for RF signals, and the operation performances thereof have a direct influence on the operation performance of the overall electronic system. However, some important parameters of the antenna such as the size, the bandwidth and the gain are restricted by the basic physical principles (e.g., the gain limit and the bandwidth limit under the limitation of a fixed size). The limits of these parameters make miniaturization of the antenna much more difficult than miniaturization of other components; and furthermore, due to complexity of analysis of the electromagnetic field of the RF component, even approximately reaching these limits represents a great technical challenge.
For a conventional antenna, the radiating operation frequency thereof is positively correlated with the size of the antenna directly, and the bandwidth is positively correlated with the area of the antenna, so the antenna usually has to be designed to have a physical length of a half wavelength. Besides, in some more complex electronic systems, an additional impedance matching network needs to be disposed at the upstream of the in feed antenna. However, the additional impedance matching network adds to the complexity in design of the feeder line of the electronic systems and increases the area of the RF system and, meanwhile, the impedance matching network also leads to a considerable energy loss. This makes it difficult to satisfy the requirement of a low power consumption in the system design. Due to the limitation of functions of the antenna themselves, most of the current antenna are applied externally to apparatuses and consume much space. Therefore, the functions and sizes of the antenna have become a technical bottleneck that hinders further reduction in volume of the apparatuses that adopt the antenna. Accordingly, how to provide a miniaturized and high-performance antenna for modern electronic integrated systems has become an important technical problem to be tackled.
Additionally, the demands for built-in antennas in various wireless communication devices become increasingly higher. For example, various electronic apparatuses such as wireless access apparatuses and wireless routers substantially all adopt external antennas, which greatly limits the room for industrial design and mechanism design of the products. Moreover, the external antennas necessitate design of a corresponding impedance matching connector and a corresponding mechanism module, which almost account for 90% or more of the cost of the whole antenna. In turn, the increased cost of the whole antenna further drives the cost of the electronic apparatus (e.g., a wireless access apparatus or a wireless router) to increase correspondingly. In contrast, using a built-in antenna will greatly save the cost of the connector and the mechanism module.